Vehicle restraints are utilized to increase safety at a loading dock. The restraints secure a truck trailer to the loading dock structure or building when goods are transferred between the trailer and the building. The restraints typically engage a rear horizontal bar referred to as the rear impact guard (RIG) or ICC bar. The RIG or ICC bar is located at the rear end of the trailer below the trailer bed. When the trailer is backed up to an available loading dock stall, the ICC bar is positioned close to the face wall of the dock. Bumpers typically extend from the face wall to protect the trailer, dock and any dock leveling fixture at the dock. Trailer restraints typically include a hooking device located in front of the dock and anchored to the dock or ground. When in use, the hooking device forms a barrier in front of the ICC bar to secure the trailer so that it cannot move away from the dock. The restraint helps avoid accidents by securing the trailer to the loading dock so that the truck driver does not inadvertently pull the trailer away when the trailer is being loaded or unloaded. The restraint also helps prevent the trailer from being pushed away from the dock during the process of loading and unloading the trailer. For example, a fork lift, particularly one carrying heavy cargo that rides onto the trailer and abruptly stops, tends to move the trailer away from the dock.
Conventional trailer restraints include storable restraints and impact restraints. Storable restraints move between a raised operating position and a lower stored position. When in the stored position, a trailer should clear the device as it is being backed into an available loading dock stall. Conventional storable restraints are disclosed in U.S. Pat. Nos. 4,488,325, 5,096,359, 4,964,777 and 7,384,229. When the trailer and dock leveler are properly positioned with the lip of the leveler resting on the trailer bed, the stored restraint is activated to rise up and securely engage the RIG. Restraint mechanisms of this style are powered into their raised position by motors, springs, or other mechanical means. Impact restraints include a movable carriage that adjusts to the height of the trailer RIG. The incoming RIG engages a sloped portion of a carriage, which pushes the carriage down and into aligned engagement with the RIG as disclosed in U.S. Pat. Nos. 4,264,259, 4,560,315 and 6,162,005. The carriage has a drive system with a motor that rotates a hook from a release position to a securing or locking position. An operator actuates the motor when the RIG engages and aligns over the carriage. The motor rotates the hook so that it emerges from the carriage and securely engages the RIG.
A problem with impact trailer restraints is that the hook drive system is susceptible to wear and tear that can produce unsafe conditions during use when the trailer is being loaded and unloaded. Slip clutches are prone to wear and require frequent replacement and servicing to prevent the hook from dropping down during use. Drive systems with a brake suffer from this same wear and tear. Even though the brake is released during use, after the hook is positioned into engagement with the RIG and the brake is applied, the brake is subject to friction and slippage in the same manner as the slip clutch system. When the slip clutch or brake is worn, the hook is not held in place with sufficient force and is susceptible to allowing the hook to inadvertently drop down and out of engagement with the RIG during use, and putting the safety of the workers at risk.
Another problem with impact trailer restraints is that the hook can be forced down and out of engagement with the RIG by certain movements of the trailer during the process of loading and unloading the trailer. The hook drive systems do not adequately accommodate the up and down, back and forth (i.e., trailer rocks toward and away from dock “dock walk”) and vibrational movements of the RIG during the loading and unloading process, such as when fork lifts move heavy cargo on and off the trailer. When the hook is engaged, the drive system does not automatically reposition the hook to accommodate these trailer movements. This can result in the hook inadvertently walking off or disengaging the RIG during use, and putting the safety of the workers at risk. Drive systems using a slip clutch or brake turn off or disengage the hook motor once the hook is raised into engagement with the RIG. However, movements of the trailer and RIG during the loading and unloading process can cause the hook to move down and disengage the RIG. Drive systems that use a brake also allow for slippage once the brake is applied during the loading and unloading process. Drive systems with a clutch or brake slip when the trailer moves from its original position during use, but do not automatically reposition the hook against the RIG when the trailer moves back to or near its original position during use, which if not corrected, can create an unsafe condition.
A further problem with trailer restraints is their harsh working environment. Vehicle restraints are mounted outside near the ground where dirt, debris, snow, ice, rain, humidity and temperature all contribute to the wear and tear on the device. The component parts of the restraints deteriorate over time, which causes binding and even the failure of the device. An impact style restraint or a trailer can be damaged when the ICC bar impacts a binding or frozen carriage and attempts to force it down. Solid debris such as rocks, wood or metal can collect beneath an impact type restraint when it is in use, which interferes with the proper movement of the carriage. In addition, attempts to protect moving parts and any sensors via a separate outer housing have been largely unsuccessful. Impact restraints require the hook to extend from the housing, the performance of which can be impaired by the harsh environment.
The present invention is intended to solve these and other problems.